This set of images of a 40-billion-mile-diameter edge-on disk encircling the young star AU Microscopii reveals a string of mysterious wave-like features. When astronomers compared images from NASA's Hubble Space Telescope, taken in 2010 and 2011, to a 2014 image from the European Southern Observatory's Very Large Telescope, they discovered the ripples are moving across the disk at a speed of 22,000 miles per hour. Such high velocities rule out the possibility that these features are caused by planets or smaller objects in the disk. Pending further research, the phenomenon remains unknown. Such structures have never before been seen in stellar gas and dust disks. The images are false-colored to bring out structural details in the disk.